Plant diversity and soil characteristics of the Ussangoda serpentine site

Serpentine soils are derived from the weathering of serpentine and ultramafic rocks, which have a high content of ferromagnesian minerals. The high content of heavy metals in serpentine soils alter their physical and chemical properties making them unsuitable for plant growth. There are six serpentine sites in Sri Lanka and the Ussangoda site is on the southern coast in Hambantota. The moisture content, organic matter and cation exchange capacity (CEC) are low in serpentine soils. The available calcium (Ca) content is low and the magnesium (Mg) content is relatively high. The Ca to Mg ratio is 0.60, which is typical for serpentine soils. Two distinct forms of vegetation grow on the Ussangoda serpentine soil. The large plain is covered by stunted, prostrate species with an extensive root system. Patches of shrubs and trees occur on the plains as small islands. The serpentine flora is sharply demarcated from the surrounding non-serpentine flora by their growth habit. The number of plant families and species is lower in the serpentine soil than in the adjacent non-serpentine areas. Four families comprising six species grew only on the serpentine soil. Five species growing in the serpentine soil contained 560 – 830 ppm of nickel (Ni) in their tissues. Hybanthus enneaspermus had 1800 ppm of nickel. Two species, Vernonia zeylanica and Scolopia acuminata, are endemic to Sri Lanka.

Keywords: Biodiversity, Evolvulus alsinoides, heavy metals, Hybanthus enneaspermus, serpentine, Ussangoda.

DOI: http://dx.doi.org/10.4038/jnsfsr.v39i4.3884

J.Natn.Sci.Foundation Sri Lanka 2011 39 (4): 355-363